2/15/2019 Kwame Nkrumah University of Science & Technology, Kumasi, Ghana Course Objectives • Understanding the fundamentals of glass technology – the thermodynamics and kinetics conditions necessary for the MSE 352 formation of glass (and glass ceramics) – the structure of glass, and the relationship between Engineering Ceramics II composition, structure, and properties 3 Credit Hours • Understanding cement chemistry and concrete Ing. Anthony Andrews (PhD) technology – Mineral aggregates, properties and testing Department of Materials Engineering – Portland cement – composition, manufacturing process, Faculty of Mechanical and Chemical Engineering hydration, properties and testing College of Engineering – Mechanical properties and testing of hardened concrete Website: www.anthonydrews.wordpress.com www.knust.edu.gh Prerequisite Recommended Books • Materials science and engineering: An introduction; 2010 – W. D. • Engineering Ceramics I (MSE 351) Callister Jr. and D. G. Rethwisch • The science and engineering of materials; 2010 - D.R. Askerland, P. P. • Phase Transformation (MSE 260) Fulay, and W. J. Wright • Fundamentals of Inorganic Glasses; 1994 - A. K. Varshneya • Physical Ceramics; 1997 – Y. -T Chiang, D. P. Birnie, W. D. Kingery • Advances in Ceramics, Volume 18-Commercial Glasses; 1986 - D. C. Boyd and J. F. MacDowell (Editors) www.knust.edu.gh www.knust.edu.gh Course Content Forms of Assessments Week Topic 1 Introduction Quizzes 10 2-3 Glass formation - Thermodynamics and Assignments 5 kinetics considerations Mid-Semester Exam 15 4-5 Glass manufacturing – composition and batch calculations End Semester Exam 70 6 Glass products Total 100 7 Mid-semester exams 8 Glass toughening 9-10 Introduction to cement technology 11-12 Introduction to concrete technology www.knust.edu.gh www.knust.edu.gh 1 2/15/2019 Introduction: Quiz 1 Classification of Engineering Materials 1. Metals and alloys – inorganic materials composed of one or 1. What are the three major classifications of ceramic materials? more metallic elements. 2. What is crystallization? 2. Ceramic and glasses – inorganic materials composed of both metallic and nonmetallic elements for which inter‐atomic 3. List two properties that may be improved by crystallization? bonding is ionic or covalent, and which are generally formed at high temperatures. 4. What is the major component in a glass? 3. Polymers – organic materials composed of long molecular chains and networks containing carbon. 4. Composites – materials where two or more of the above materials are brought together on a macroscopic scale. www.knust.edu.gh www.knust.edu.gh Introduction: Characteristics of Ceramic Materials Classification of Ceramics • Usually a compound between metallic and nonmetallic elements Abrasive Ceramics? • Desirable properties achieved through a high temperature heat Properties? treatment process (firing). • Bonds are partially or totally ionic, and can have combination of ionic and covalent bonding • Generally hard and brittle • Generally electrical and thermal insulators • Traditional ceramics – based on clay (china, bricks, tiles, porcelain), glasses. www.knust.edu.gh www.knust.edu.gh Ceramic Crystal Structures Ceramic Crystal Structures • Similar to metal crystal structures but with one important 1. Charge neutrality difference… – the bulk ceramic must remain electrically neutral – In ceramics, the lattice sites are occupied by IONS – this means the NET CHARGE must sum to ZERO • CATIONS: positively charged ions (the smaller of the two) – electron loss TO the more electronegative atom 2. Coordination number (CN) – cations are usually metals, from the left side of the periodic table – CN ≡ number of nearest-neighbor atoms – as r /r increases, the cation’s CN also increases • ANIONS: negatively charged ions (the larger of the two) c a – electron gain FROM the more electropositive atom – anions are usually non-metals, from the right side of the periodic table www.knust.edu.gh www.knust.edu.gh 2 2/15/2019 Coordination Number Coordination Number • The stability of the crystal structure is influenced by the ion • What’s so important about CN? contact. – CN determines the possible crystal structures • Since CN determines crystal structure, and crystal structure determines physical properties, therefore, CN determines physical properties • The most common coordination numbers for ceramics are 4, 6, and 8. www.knust.edu.gh www.knust.edu.gh Coordination Silicate Ceramics Number • Composed mainly of silicon and oxygen, the two most abundant elements in earth’s crust (rocks, soils, clays, sand) • Larger coordination numbers 4- • Basic building block: SiO4 tetrahedron correspond to larger cation ions. • Si-O bonding is largely covalent, but overall SiO4 block has charge of –4 4- • Rationale?? • Various silicate structures – different ways to arrange SiO4 blocks www.knust.edu.gh www.knust.edu.gh Silicate Structures Silica = silicon dioxide = SiO2 Silicates are classified on the basis of Si-O polymerism • Every oxygen atom is shared by adjacent tetrahedra. 4- [SiO4] Isolated tetrahedra Nesosilicates Examples: olivine garnet Regular and orderly 6- arrangement of tetrahedra units [Si2O7] Paired tetrahedra Sorosilicates Examples: lawsonite produce crystalline structure. 2- n[SiO3] n = 3, 4, 6 Ring silicates Fused Silica or Vitreous Silica Cyclosilicates Examples: benitoite BaTi[Si3O9] axinite Ca3Al2BO3[Si4O12]OH www.knust.edu.gh www.knust.edu.gh 3 2/15/2019 Glass Structure Glass Structure • Basic Unit: Glass is noncrystalline (amorphous) 4- • Fused silica is SiO2 to which no SiO4 tetrahedron impurities have been added Si4+ • Other common glasses contain + 2+ O2- impurity ions such as Na , Ca , Al3+, and B3+ Na+ • Quartz is crystalline Si4+ SiO2: O2- 2-D of: (a) crystalline structure of silica; (b) amorphous structure of (soda glass) silica glass; (c) soda silica glass. www.knust.edu.gh www.knust.edu.gh Differences between crystalline Characteristics of Glasses and amorphous solids • Glass is an amorphous solid with the structure of a liquid. • Glass has no distinct melting or freezing point - similar to that of amorphous alloys and amorphous polymers. 1. Structure of atoms • Most glasses are produced by adding other oxides (e.g. 2. Phase transformation CaO, Na2O) whose cations are incorporated within SiO4 behaviour network. • Some other oxides (TiO2, Al2O3) substitute for silicon Phase transformation of crystalline and and become part of the network. amorphous solids on heating www.knust.edu.gh www.knust.edu.gh Composition of Glasses Examples of Glasses • All glasses contain at least 50% silica, which is known as a glass former. 1. Soda Lime Glass – General purpose glass – Other network formers - B2O3, GeO2 – Lowest cost • The composition and properties of glasses can be – E.g window glass modified greatly by the addition of various other elements. 2. Borosilicate Glass – Very resistant to chemical attack • The additives act as intermediates (TiO2, Al2O3) or – Easy to cut modifiers (CaO, Na2O). – High luminous transmission – E.g. touch control panels, LCD, solar cells • Additives role? www.knust.edu.gh www.knust.edu.gh 4 2/15/2019 Examples of Glasses Glass State: Solid or Liquid? 3. Lithium Potash Borosilicate Glass – Relatively high operating temperature – Low coefficient of thermal expansion – Excellent sealing characteristics • Usually when a liquid is – Microwave window applications cooled to below its melting point, crystals form and it 4. Glass Ceramics solidifies. – Have a high crystalline component to their microstructure. – They have a near-zero coefficient of thermal expansion. – They are strong because of the absence of the porosity found in conventional ceramics. Molecular arrangement in a – Uses are cookware, heat exchangers, gas turbine engines crystal www.knust.edu.gh www.knust.edu.gh Glass State: Solid or Liquid? Glass State: Solid or Liquid? • Glass is a liquid which does not crystallize at lower • If the viscosity rises temperatures below its melting point (metastable state). enough as it is cooled further, it may never crystallize. • Glasses are ceramic materials with the amorphous structure of a frozen liquid. • The molecules then have a disordered arrangement, but • Thus any material including metals and water can be sufficient cohesion to made into a glass when cooled rapidly. maintain some rigidity. molecular arrangement in a glass Therefore is glass a solid or a liquid?? www.knust.edu.gh www.knust.edu.gh Glass Formation Glass Formation Upon sufficiently fast cooling to • Specific volume (1/ρ) vs Temperature (T): a low enough temperature nearly any material can form a glass. • Crystalline materials: Specific volume -- crystallize at melting temp, Tm -- have abrupt change in spec. • “sufficiently fast” to ensure Supercooled Liquid Liquid (disordered) vol. at T that while traversing the Tm to m Tg temperature range, there is insufficient time to crystallize. Glass • Glasses: (amorphous solid) -- do not crystallize Crystalline -- change in slope in spec. vol. • “low enough” to ensure that (i.e., ordered) solid curve at Tg the sample is brought to T< Tg T Tg Tm -- transparent - no grain boundaries Vitrification to scatter light www.knust.edu.gh www.knust.edu.gh 5 2/15/2019 Glass Formation 1. From the vapour state – by condensing the vapour of the material onto a cold substrate. 2. From the liquid state – quenching from the melt. The rate of quenching required depends on the material. 3. In the solid state – by severely deforming the crystals, amorphous state can be obtained. Ball milling has been one of the popular examples for this method (for alloys). www.knust.edu.gh 6.